The mechanism of intracellular pH regulation will be elucidated for a variety of glycolyzing cell types including epithelial cell lines, transformed cell lines and renal tubule segments such as the collecting duct. Cell metabolism, especially lactate production from glycolysis, is the major acid load of these cells. Thus, mechanisms for lactate and proton efflux will be analyzed and related to the cells' metabolic status. The plasma membrane fluxes of protons and lactate and their electrochemical gradients will be measured to characterize the transport processes as active of passive. The carrier(s) involved will be characterized in terms of ion requirements, functional chemical sites, and competitive and noncompetitive interaction with inhibitors.